Emergency department visits peaked during the week ending 12/31/21 and have since dropped rapidly. Hospital admissions peaked one week later and are declining gradually.
Trend in Hospital Admissions Has Lagged 1 Week Behind ED Visits.
We continue to follow a cohort of 250 hospitals treating a high volume of COVID-19 patients, located in 164 counties in the United States. Within this cohort, emergency department visits for COVID-19 began to rise rapidly by the week ending 12/17/21 and reached a peak of 230.5 thousand during the week ending 12/31/21. Since then, ED visits have declined precipitously, with 140.6 thousand reported during the most recent week ending 1/21/22.
The trend in hospital admissions for COVID-19 has lagged about 1 week behind ED visits, reaching a peak of 29.3 thousand during the week ending 1/7/22. Since then, hospital admissions for COVID-19 have declined more gradually, with 24.2 thousand reported during the week ending 1/21/22.
Interpreting the Data
During the recent wave dominated by the Omicron variant of SARS-CoV-2, new infections have been vastly underreported. As a result of a surge in home-based rapid testing and the rapid growth in asymptomatic cases, only 1 in 4 cases of COVID-19 are now being reported by public authorities. While ED visits represent an even smaller fraction of all COVID-19 cases, the rapid rise and fall seen above likely mirrors the underlying trend in disease incidence.
Since it takes time before the initial symptoms of COVID-19 become severe enough to require hospitalization, we would expect to see a lag between ED visits and hospital admissions. The fact that hospital admissions have been declining more slowly suggests that the lag-time between initial symptoms and subsequent hospitalization is quite variable.
The Evidence Does Not Support the Incidental Admissions Hypothesis.
A number of reports have suggested that as many as one-half of all hospital inpatients identified as COVID-positive are incidental cases who were admitted for reasons other than their viral infections. If these reports were accurate, we would have expected the hospital admissions curve to look a lot more like the ED visits curve.
The observed lag in the hospital admissions curve provides strong evidence that the large majority of such admissions are not incidental.
We will continue to follow ED visits and hospitalizations for COVID-19 in our cohort of 250 sentinel hospitals.
Technical Notes: Sentinel Hospital Cohort
We are following a cohort of 250 high-volume hospitals located in 164 counties throughout the U.S. Our focus on a cohort of hospitals known to have treated large numbers of COVID-19 patients avoids problems of sampling variability and inconsistent reporting among smaller, lower-volume hospitals. The data were derived from COVID-19 Reported Patient Impact and Hospital Capacity by Facility, posted by the U.S. Department of Health and Human Services (HHS). The database is updated weekly. The most recent update, on which this article is based, covers the week ending 1/21/22.
The data on emergency department visits for COVID-19 are based upon the variable previous_day_covid_ED_visits_7_day_sum, defined as “Sum of total number of ED visits who were seen on the previous calendar day who had a visit related to COVID-19 (meets suspected or confirmed definition or presents for COVID diagnostic testing – do not count patients who present for pre-procedure screening) reported in 7-day period.”
We calculated hospital admissions for COVID-19 as the sum of two variables:
- previous_day_admission_adult_covid_confirmed_7_day_sum, defined as “Sum of number of patients who were admitted to an adult inpatient bed on the previous calendar day who had confirmed COVID-19 at the time of admission reported in the 7-day period.”
- previous_day_admission_pediatric_covid_confirmed_7_day_sum, defined as “Sum of number of pediatric patients who were admitted to an inpatient bed, including NICU, PICU, newborn, and nursery, on the previous calendar day who had confirmed COVID-19 at the time of admission.”
Both of these definitions are confined to admitted patients who were diagnosed with confirmed COVID-19 at the time of admission, and thus tend to attenuate the potential problem of so-called incidental admissions.
The locations of 249 of the 250 sentinel hospitals are mapped below.